A variety of material dispensers have been developed including those directed at dispensing foamable material such as polyurethane foam which involves mixing certain chemicals together to form a polymeric product while at the same time generating gases such as carbon dioxide and water vapor. If those chemicals are selected so that they harden following the generation of the carbon dioxide and water vapor, they can be used to form “hardened” (e.g., a cushionable quality in a proper fully expanded state) polymer foams in which the mechanical foaming action is caused by the gaseous carbon dioxide and water vapor leaving the mixture. In particular techniques, synthetic foams such as polyurethane foam are formed from liquid organic resins and polyisocyanates in a mixing chamber (e.g., a liquid form of isocyanate, which is often referenced in the industry as chemical “A”, and a multi-component liquid blend called polyurethane resin, which is often referenced in the industry as chemical “B”). The mixture can be dispensed into a receptacle, such as a package, a mold, a product recess or a foam-in-place bag (see e.g., U.S. Pat. Nos. 4,674,268, 4,800,708 and 4,854,109), where it reacts to form a polyurethane foam.
With respect to dispensers using urethane-foam for packaging applications, the first practical hand-held dispensers are believed to have become commercially available in the late 1960's. These designs were considered an advancement compared to the massive, complicated, and messy urethane dispensing machinery available prior to that time. Initially, almost all components of a dispenser were built into a single housing, which was relatively bulky. This large housing incorporated a pneumatic drive cylinder, a mixing chamber with ports, a valving rod, and a solvent chamber—only the handle (with trigger) was a separate item. The single housing dispenser was easy to service or change, but it was an expensive item, as the entire drive mechanism had to be returned for service every time a mixing chamber wore out, or an operator was not able to clean a clogged chemical port.
Because of the high cost of these dispensers, return programs were set up, so that customers could return the used dispenser units to the factory for credit and refurbishment. This quickly became a logistical, and a cost accounting nightmare.
A subsequent technology modification was the introduction of the cartridge gun. The cartridge was a separable item from the drive cylinder, and it incorporated the items that were most prone to failure—the chemical ports and mixing chamber. This meant that there was a lot less to discard when a failure occurred. The cartridges were very inexpensive compared to the old style gun units, and were intended to be throwaway item. This eliminated the above noted logistical and accounting nightmare, but the customer still had to purchase cartridges whenever they became inoperable, and thus was still a source of expense. The typical cartridge oriented dispenser design during this time frame was pneumatically driven, and required that the customer have a clean and dry supply of compressed air with a line pressure typically between 80 and 120 psi. Air driven dispensers have some advantages as in being simple, easy to understand design, easy to maintain, and inexpensive to manufacture. Air driven dispenser also have some limitations, however, such as:
a) Limited to locations that provide compressed air to power them—this would often require the operator to invest in, and install a shop air compressor.
b) Shop air driven power is very inefficient, some estimates put the efficiency factor at 10%. Consequently, it is very expensive to run air-powered equipment.
c) These dispensers did not operate properly if shop air pressure was too low—they will be unable to generate enough force to open the cartridge.
d) Even with adequate air pressure, pneumatic guns have a relatively low opening force, compared to electric drive dispensers that were developed in later years.
e) Cartridges, as they are used, develop a build-up of urethane on the inside diameter (“ID”) of the mixing chamber, which gradually increases the level of force required to open the cartridge. Consequently, the relatively low opening force limits the service life of the cartridge, since it is useless if it can no longer be opened by the drive system.
f) Air driven dispensers are sensitive to water in the air supply lines—which can wash the lubrication out of the sliding seals—and leak into the A chemical container from the pumps, and also are sensitive to oil and rust in the compressed air supply lines.
g) These prior art pneumatic dispensers are also not robust in the workplace, and required frequent maintenance and repair.
In most settings, the problems associated with these air driven systems were deemed by the operators to outweigh the advantages. Accordingly, “All electric” systems appeared in the field, and, were deemed an improvement by some over the air driven systems such that many a typical hand-held dispenser today is a cartridge based, all-electric mechanism. In some conventional hand held dispensers, there is utilized an electric motor driven ball screw which opens and closes the valving rod in the mixing module to turn the flow of foam on and off, and these typical conventional hand-held dispenser mechanisms have the following components:
Drive Motor—DC Brush Type—24 to 36 volts—rare earth magnets for highest power in the smallest package;
Ball Screw—translates the rotary motion of the motor into linear motion that moves the valving rod;
Gear Train—connects the motor shaft to the shaft of the ball screw;
Handle—for user to hold while dispensing foam—contains the trigger switch and trigger boot;
Manifold—mounted to the handle, the manifold typically provides the mechanical backbone of the dispenser—supporting the drive system and the mixing module, and connecting to the chemical hoses that come from the pumps;
Mixing Module—The component that mixes the two foam precursor chemicals A and B together to initiate the foaming process;
Manifold Heater—attempts to keep the manifold temperature close to the chemical's operating temperature to minimize the cold-shot effect—where the two chemicals do not mix well at the start of a shot because they have sat in an unheated manifold for an extended period;
Trigger Switch and Boot—mounted inside the handle, the trigger starts and stops the dispensation of foam—the boot is a flexible cover designed to protect the trigger and to provide comfort for the user's finger;
Small Filter Screens—mounted in the flow paths of the manifold, these removable wire mesh screens protect the orifice ports in the mixing module from particulates in the chemical;
Cable Strain Relief—for the umbilical cable that connects the dispenser to the control console (intended to prevent damage from pulling, twisting, or bending of the cable during routine use) mounted on the rear of the handle.
The electric driven hand held dispensers thus have some advantages over the air driven systems in avoiding some of the above noted problems associated with air driven systems, but the electric driven systems (as well as many other current hand held dispenser designs in general) also suffer from a variety of drawbacks. For example, the placement and/or sizing of components of many of the prior art designs as in the shutoff valves, swivel fittings, port plug and filter screens provide for a bulky, non-slender handheld design with associated drawbacks as in poor operator ergo-dynamics (e.g., poor balancing in hand), poor visibility and container accessing limitations, as well as high susceptibility to chemical contamination of dispensed product build-up on those components. Additionally, many of the prior art designs involve small area filter elements and typical electric driven hand held dispensers are prone to failure as in freewheeling failures and gear failures, lack of sufficient power to avoid freeze ups despite having driving systems that often present bulky and excessive component drive transmissions. Additional drawbacks associated with typical conventional designs include non-robust trigger switches, poor electrical power line dispenser connections, poor chemical heater performance (when provided at all) in the hand held dispenser, low volume solvent feeding systems and inefficient mixing module mounting systems.